1. Field of the Invention
The invention relates to methods for purification of Vaccinia viruses (VV) and/or Vaccinia virus (VV) particles.
2. Description of Related Art
Traditionally in medicine, a vector is a living organism that does not cause disease itself, but which spreads infection by “carrying” pathogens (agents that cause disease) from one host to another. A vaccine vector is a weakened or killed version of a virus or bacterium that carries an inserted antigen (coding for a protein recognized by the body as foreign) from a disease-causing agent to the subject being vaccinated. A vaccine vector delivers the antigen in a natural way into the body and stimulates the immune system into acting against a “safe infection.” The immune system is led into generating an immune response against the antigen that protects the vaccinated subject against future “risky infections.”
In vaccine development, a recombinant modified virus can be used as the vehicle or vaccine vector for delivering genetic material to a cell. Once in the cell, genetic information is transcribed and translated into proteins, including the inserted antigen targeted against a specific disease. Treatment is successful if the antigen delivered by the vector into the cell produces a protein, which induces the body's immune response against the antigen and thereby protects against the disease.
A viral vector can be based on an attenuated virus, which cannot replicate in the host but is able to introduce and express a foreign gene in the infected cell. The virus or the recombinant virus is thereby able to make a protein and display it to the immune system of the host. Some key features of viral vectors are that they can elicit a strong humoral (B-cell) and cell-mediated (T-cell) immune response.
Viral vectors are commonly used by researchers to develop vaccines for the prevention and treatment of infectious diseases and cancer, and of these, poxviruses (including canary pox, vaccinia, and fowl pox) are the most common vector vaccine candidates.
Pox viruses are a preferred choice for transfer of genetic material into new hosts due to the relatively large size of the viral genome (appr. 150/200 kb) and because of their ability to replicate in the infected cell's cytoplasm instead of the nucleus, thereby minimizing the risk of integrating genetic material into the genome of the host cell. Of the pox viruses, the vaccinia and variola species are the two best known. The virions of pox viruses are large as compared to most other animal viruses (for more details see Fields et al., eds., Virology, 3rd Edition, Volume 2, Chapter 83, pages 2637 ff).
Variola virus is the cause of smallpox. In contrast to variola virus, vaccinia virus does not normally cause systemic disease in immune-competent individuals and it has therefore been used as a live vaccine to immunize against smallpox. Successful worldwide vaccination with Vaccinia virus culminated in the eradication of smallpox as a natural disease in the 1980s (The global eradication of smallpox. Final report of the global commission for the certification of smallpox eradication; History of Public Health, No. 4, Geneva: World Health Organization, 1980). Since then, vaccination has been discontinued for many years, except for people at high risk of poxvirus infections (for example, laboratory workers). However, there is an increasing fear that, for example, variola causing smallpox may be used as a bio-terror weapon. Furthermore, there is a risk that other poxviruses such as cowpox, camelpox, and monkeypox may potentially mutate, through selection mechanisms, and obtain similar phenotypes as variola. Several governments are therefore building up stockpiles of Vaccinia-based vaccines to be used either pre-exposure (before encounter with variola virus) or post-exposure (after encounter with variola virus) of a presumed or actual smallpox attack.
Vaccinia virus is highly immune-stimulating and provokes strong B-(humoral) and T-cell mediated immunity to both its own gene products and to any foreign gene product resulting from genes inserted in the Vaccinia genome. Vaccinia virus is therefore seen as an ideal vector for vaccines against smallpox and other infectious diseases and cancer in the form of recombinant vaccines. Most of the recombinant Vaccinia viruses described in the literature are based on the fully replication competent Western Reserve strain of Vaccinia virus. It is known that this strain has a high neurovirulence and is thus poorly suited for use in humans and animals (Morita et al. 1987, Vaccine 5, 65-70).
In contrast, the Modified Vaccinia virus Ankara (MVA) is known to be exceptionally safe. MVA has been generated by long-term serial passages of the Chorioallantois Vaccinia Ankara (CVA) strain of Vaccinia virus on chicken embryo fibroblast (CEF) cells (for review see Mayr, A. et al. 1975, Infection 3, 6-14; Swiss Patent No. 568,392). Examples of MVA virus strains deposited in compliance with the requirements of the Budapest Treaty are strains MVA 572, MVA 575, and MVA-BN® deposited at the European Collection of Animal Cell Cultures (ECACC), Salisbury (UK) with the deposition numbers ECACC V94012707, ECACC V00120707 and ECACC V00083008, respectively, and described in U.S. Pat. Nos. 7,094,412 and 7,189,536.
MVA is distinguished by its great attenuation profile compared to its precursor CVA. It has diminished virulence or infectiousness, while maintaining good immunogenicity. The MVA virus has been analyzed to determine alterations in the genome relative to the wild type CVA strain. Six major deletions of genomic DNA (deletion I, II, III, IV, V, and VI) totaling 31,000 base pairs have been identified (Meyer, H. et al. 1991, J. Gen. Virol. 72, 1031-1038). The resulting MVA virus became severely host-cell restricted to avian cells. The excellent properties of the MVA strain have been demonstrated in extensive clinical trials (Mayr, A. et al. 1978, Zbl. Bakt. Hyg. I, Abt. Org. B 167, 375-390; Stickl, H. et al. 1974, Dtsch. med. Wschr. 99, 2386-2392), where MVA 571 has been used as a priming vaccine at a low dose prior to the administration of conventional smallpox vaccine in a two-step program and was without any significant adverse events (SAES) in more than 120,000 primary vaccinees in Germany (Stickl, H et al. 1974, Dtsch. med. Wschr. 99, 2386-2392; Mayr et al. 1978, Zbl. Bakt. Hyg. I, Abt. Org. B 167, 375-390).
MVA-BN® is a virus used in the manufacturing of a stand-alone third generation smallpox vaccine. MVA-BN® was developed by further passages from MVA strain 571/572. To date, more than 1500 subjects including subjects with atopic dermatitis (AD) and HIV infection have been vaccinated in clinical trials with MVA-BN® based vaccines.
The renewed interest in smallpox vaccine-campaigns with Vaccinia-based vaccines has initiated an increased global demand for large-scale smallpox vaccine production. Furthermore, the use of Vaccinia virus as a tool for preparation of recombinant vaccines has additionally created significant industrial interest in methods for manufacturing (growth and purification) of native Vaccinia viruses and recombinant-modified Vaccinia viruses.
Viruses used in the manufacturing of vaccines or for diagnostic purposes can be purified in several ways depending on the type of virus. Traditionally, purification of pox viruses including Vaccinia viruses and recombinant-modified Vaccinia viruses has been carried out based on methods separating molecules by means of their size differences. To enhance removal of host cell contaminants (e.g. DNA and proteins), in particular DNA, the primary purification by means of size separation has been supplemented by secondary methods such as enzymatic digestion of DNA (e.g. Benzonase treatment). Most commonly, the primary purification of Vaccinia viruses and recombinant-modified Vaccinia viruses has been performed by sucrose cushion or sucrose gradient centrifugation at various sucrose concentrations. Recently, ultrafiltration has also been applied either alone or in combination with sucrose cushion or sucrose gradient purification.
Vaccinia Viruses-based vaccines have in general been manufactured in primary CEF (Chicken Embryo Fibroblasts) cultures. Vaccines manufactured in primary CEF cultures are generally considered safe as regards residual contaminants. First, it is scientifically unlikely that primary cell cultures from healthy chicken embryos should contain any harmful contaminants (proteins, DNA). Second, millions of people have been vaccinated with vaccines manufactured on CEF cultures without any adverse effects resulting from the contaminants (CEF proteins and CEF DNA). There is, therefore, no regulatory requirement for the level of host cell contaminants in vaccines manufactured in primary CEF cultures, but for each vaccine the manufacturer must document its safety. The regulatory concern for vaccines manufactured in primary CEF cultures relates to the risk of adventitious agents (microorganisms (including bacteria, fungi, mycoplasma/spiroplasma, mycobacteria, rickettsia, viruses, protozoa, parasites, TSE agent) that are inadvertently introduced into the production of a biological product).
In the current methods for purification of Vaccinia viruses, manufactured in primary CEF culture the level of CEF protein may be up to 1 mg/dose and the CEF DNA level may exceed 10 μg/dose of 1×108 as measured by the TCID50. These levels are considered acceptable from a safety and regulatory perspective as long as the individual vaccine manufacturer demonstrates that the levels to be found in the Final Drug Product (FDP) are safe at the intended human indications. Due to the risk of presence of adventitious agents in vaccines manufactured in primary cell cultures and the associated need for extensive, expensive biosafety testing of each vaccine batch manufactured, there is a strong stimulus for the vaccine industry to change to continuous cell lines. Once a continuous cell line has been characterized the need for testing for adventitious agents of the production batches is minimal.
However, switch from primary to continuous cell culture for production of Vaccinia and Vaccinia recombinant vaccines is expected to impose stricter safety and regulatory requirements. In fact, the regulatory authorities have proposed new requirements for levels of DNA contaminants in vaccines manufactured using continuous cell lines (See Draft FDA guideline), which may be as low as 10 ng host-cell DNA/dose. To achieve such low level of host cell contaminants, new and improved methods for purification are needed.
It appears that vaccinia virions are able to bind to heparin through the surface protein A27L (Chung et al. 1998, J. Virol. 72, 1577-1585). At least three surface proteins A27L (Chung et al., J. Virol. 72(2):1577-1585, 1998; Ho et al., Journal of Molecular Biology 349(5):1060-1071, 2005; Hsiao et al., J. Virol. 72(10):8374-8379, 1998) D8L (Hsiao et al., J. Virol. 73(10):8750-8761, 1999), and H3L (Lin et al., J. Virol. 74(7):3353-3365, 2000) of the most abundant infectious form of the Vaccinia virus have been reported to bind to glycosaminoglycans.
It has further been suggested that affinity chromatography (Zahn, A and Allain, J.-P. 2005, J. Gen. Virol. 86, 677-685) may be used as basis for purification of certain virus preparations. There are several examples for the application of ion exchange and affinity membrane adsorbers (MA) for the purification of virus particles like adenoviral vectors (Peixoto et al., Biotechnology Progress 24(6):1290-1296, 2008; Sellick, BioPharm International 19(1):31-32, 34, 2006), Aedes aegyptidensonucleosis virus (Enden et al., J Theor Biol 237(3):257-264, 2005), baculovirus (Wu et al., Hum. Gene Ther. 18(7):665-672, 2007), and influenza virus (Kalbfuss et al., Journal of Membrane Science 299(1-2):251-260, 2007; Opitz et al., Biotechnol. and Bioeng. 103(6):1144-1154, 2009; and Opitz et al., Journal of Biotechnology 131(3):309-317, 2007).
For efficient purification of vaccinia virus and recombinant vaccinia virus-based vaccines, some significant challenges need to be overcome. Vaccinia virions are far too large to be effectively loaded onto commercially available heparin columns, e.g., the Hi-Trap heparin column from Amersham Biosciences used by others (Zahn, A and Allain, J.-P. 2005, J. Gen. Virol. 86, 677-685) for lab-scale purification of Hepatitis C and B viruses. The Vaccinia virion volume is approximately 125 times larger than Hepatitis virion. (The diameter of the Vaccinia virus is, thus, appr. 250 nm as compared with the hepatitis C and B virions diameter being appr. 50 nm). Thus, available matrices as, e.g., used in the column-based approach may not allow for adequate entrance of virions into the matrix, loading of sufficient amounts of virus particles or sufficiently rapid flow through the column to meet the needs for industrial scale purification. Zahn and Allain worked with virus load up to 1×106 in up to 1.0 ml volume. For pilot-scale purification to achieve sufficient material for early clinical trials virus loading capacity higher than 1×1011, preferably up 1×1013, in volumes higher than 5 L, preferably up to 50 L, is needed. For industrial purification of Vaccinia virus loading capacity higher than 1×1013, preferably higher than 1×1014 in volumes higher than 300 L, preferably higher than 600 L, is needed.
The large size of the Vaccinia virus may prevent effective steric access between the specific surface proteins of the virions and the ligand immobilized to the matrix. Currently described lab-scale methods of use for purification of small virus particles may therefore not be industrially applicable to purification of Vaccinia virus.
Due to the high number of functional surface molecules interacting with the ligand used for binding of the Vaccinia virus particles, elution of bound Vaccinia virus may require more harsh and therefore potentially denaturing conditions to elute and recover the Vaccinia virus particles in a biologically effective form in high yields. The matrix, the ligand design, the method of ligand immobilization, and the ligand density may therefore require careful design to mediate an effective binding of the Vaccinia virus and to permit an effective elution of biologically active Vaccinia virus particles.
Vaccinia virions are too large to be sterile filtered. The method used in this invention has therefore been developed by to be applicable for an aseptic industrial-scale manufacturing process in a way ensuring full compliance with regulatory requirements regarding sterility of vaccines. In line with the above and for the purpose of this invention, the column substituted with the ligand should be applicable for sterilization-in-place or should be available as a pre-sterilized unit.
The introduction of cell culture-derived smallpox vaccines required an adaptation of the original downstream processing schemes. Current smallpox vaccines like e.g. ACAM2000 are purified mainly after cell disruption by centrifugation and filtration methods (Abdalrhman et al., Vaccine 24(19):4152-4160, 2006; Greenberg and Kennedy, Expert Opinion on Investigational Drugs 17(4):555-564, 2008; and Monath et al., International Journal of Infectious Diseases 8(Supplement 2):31-44, 2004). The disadvantage of these methods is the limited depletion of contaminants like host cell DNA and proteins. In order to comply with regulatory expectations for current human smallpox vaccines based on continuous cell lines a nuclease treatment for host cell DNA depletion is often included in these processes (Greenberg and Kennedy, 2008; and Monath et al. 2004).
Examples of glycosaminoglycans in affinity chromatography applications are heparin and heparan sulfate. These are highly charged, linear and sulfated polysaccharides composed of repeating disaccharide units containing an uronic acid (glucuronic or iduronic acid) and an N-sulfated or N-acetylated glucosamine (Ampofo et al., Analytical Biochemistry 199(2):249-255, 1991; Nugent, Proceedings of the National Academy of Sciences of the United States of America 97(19):10301-10303, 2000; Rabenstein, Nat. Prod. Rep. 19:312-331, 2002).
Cellufine® sulfate and sulfated cellulose membranes are sulfated glucose polymers. Several studies reported antiviral activities of sulfated cellulose and sulfated dextran/dextrines (Baba et al., Antimicrob. Agents Chemother. 32(11):1742-1745, 1988; Chattopadhyay et al., International Journal of Biological Macromolecules 43(4):346-351, 2008; Mitsuya et al., Science 240(4852):646-649, 1988; Piret et al., J. Clin. Microbiol. 38(1):110-119, 2000), as well as the binding of virus particles to Cellufine® sulfate (O'Neil et al., Bio/Technology 11:173-178, 1993; Opitz et al., Biotechnol. and Bioeng. 103(6):1144-1154, 2009). The precise interaction between these viruses and sulfated cellulose is currently not fully understood.
To achieve a bio-specific purification of Vaccinia virus particles with high biological activity, there is a need in the art for development of industrially usable ligands identical to or very similar to the presumed native ligand for Vaccinia target cell entry. Thus, use of a ligand displaying highly specific and highly effective binding to the Vaccinia virus would be advantageous as it would improve purification by its ability to specifically sort out biologically active Vaccinia virus particles thereby increasing the purity, viability, and functionality of the purified Vaccinia virus.